Recovering metals from complex metal sulfides

Methods for recovering base metals, including, among other metals, molybdenum and nickel, from metal sulfides containing a Group VIB metal and a Group VIII metal. Generally, the methods comprise: contacting metal sulfides with a leaching solution containing ammonia and air to dissolve the metals into the leaching solution, forming a slurry containing soluble complexes of the metals, ammonium sulphate and solid residue containing ammonium metavanadate and any carbonaceous materials. The solid residue containing ammonium metavanadate and carbonaceous materials is then separated from the slurry and metal complexes are precipitated from the slurry by adjusting the pH. A second slurry may be formed comprising a second solid residue and a primary filtrate comprising ammonium sulfate solution that is substantially free of metals. The second solid residue is separated from the primary filtrate comprising ammonium sulfate by any means suitable for separation of solids from liquids and is then dissolved, at a second pre-selected pH, to form a Group VIB metal precipitate and a Group VIII metal containing solution. Group VIB and Group VIII metals can be easily recovered from the precipitate and solution, respectively. In some embodiments Group VB metals are recovered as well.